After quietly creeping up behind Sen and shoving him to his death, the portly perp then fled down the station’s stairs onto Queens Boulevard.

The victim had been looking westbound as the subway was approaching from the east, said Police Commissioner Ray Kelly.

“We’re still investigating. There were some witnesses on the platform. We’re getting some hotline tips,” Kelly added.

“We’re reasonably confident that we’ll identify the suspect. We are properly deployed in transit areas.”

Kelly said investigators were able to identify Sen using “information on his person and info called in.”

Cops found Sen’s laptop and wallet at the scene, a law enforcement source previously said. Sen’s mangled body was wedged underneath the second car.

Despite last night’s random attack being the second such nightmare to unfold on the city’s subway lines in the last month, Mayor Bloomberg assured residents that the city’s vast underground transportation network system is still safe.

“It’s the safest big transit system in the world…5.5 million people use it everyday. Cameras wouldn’t prevent what happened yesterday.”

The killer was recorded on surveillance footage from a nearby pizzeria running down 40th Street.

“I don’t know if there’s a way to prevent it. There’s always going to be a deranged person. But two is too many,” he said.

On Dec. 3, drifter Naeem Davis, 30, allegedly shoved Queens dad Ki Suk Han, 58, into the path of a Q train at the 49th Street station in Manhattan. Davis is being held on murder charges.

“ Our prayers go out to the families in these cases,” said Bloomberg. “It’s a rare occurrence and shouldn’t change our lifestyle. Everybody should exercise caution…you are so much safer here than anyway else.”

The mayor’s words were little comfort to Sen’s roommates who recalled him as a “quiet man” who “loved music” and “worked seven days a week.”

“I feel very much shocked,” said Suman.

Suman said that Sen — who was single and had no kids — had just opened a copy shop on Manhattan’s Upper West Side.

“My heart is broken because this guy was so nice and quiet,” added Sen’s other roommate, MD Khan, 33, a taxi driver.